The effect of cigarette smoke constituents on the expression of HLA-DR in orbital fibroblasts derived from patients with Graves ophthalmopathy

Numerous studies have established a strong association between smoking and Graves disease, but the underlying mechanism of Graves ophthalmopathy has not been elucidated. Recent studies of Graves ophthalmopathy have focused on the orbital fibroblast as an integral component in the pathogenesis of this disorder. This investigation focuses on the effect of cigarette smoke constituents, nicotine and tar, to alter the expression of human leukocyte antigen (HLA-DR) in cultured orbital fibroblasts from patients with Graves disease. HLA-DR expression was quantified by scanning densitometry of whole cell lysates subjected to sodium dodecyl sulfate--polyacrylamide gel electrophoresis with immunoblotting and also by direct immunofluorescence. Cultured orbital fibroblasts, obtained from patients undergoing orbital decompression for severe Graves ophthalmopathy, failed to express HLA-DR as analyzed by both immunoblotting and direct immunofluorescence when treated with nicotine alone (25-300 ng/ml). The expression of HLA-DR increased three-fold when nicotine (25 ng/ml) in combination with interferon-gamma (500 U/ml) was added to the cultured orbital fibroblasts (p < 0.0001). Cultured orbital fibroblasts treated with tar alone (60-600 ng/ml) failed to exhibit HLA-DR expression as assessed by direct immunofluorescence and immunoblotting. A greater than two-fold increase in HLA-DR expression occurred when tar (600 ng/ml) combined with interferon-gamma (500 U/ml) was added to the cultured orbital fibroblasts (p < 0.0001). The results suggest a possible molecular mechanism for the more severe ophthalmopathy observed in Graves patients who smoke cigarettes. These findings could prove useful for possible medical interventions to decrease or even inhibit the interaction between cigarette constituents, cytokines, and orbital fibroblasts.